Wordzen - We write your emails for you. Literally.
Grammarly - Clear, effective, mistake-free writing everywhere you type.
InboxVudu - Spend 90% less time on e-mail.
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Mailbutler - Mailbutler adds lacking functionality to email clients and increases your productivity
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.